1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory, such as flash memory, for preventing the unauthorized reproduction of data stored in a main storage region.
2. Description of the Related Art
Flash memory, which is nonvolatile semiconductor memory, is able to write (program) and erase data electrically, and is widely used because stored data is not lost even when the power is turned OFF. For example, it is becoming popular as a memory card for storing music data distributed for a fee via the Internet. Further, it has also come into widespread use as memory for storing data and programs specific to cellular telephones and other compact information terminals.
To prevent the unauthorized copying of music data, and specified data or programs stored in the above-mentioned flash memory, and to prevent the use of flash memory in illegally obtained data equipment, an unauthorized copying prevention function, and an unauthorized use prevention function are required. These functions are achieved, for example, by providing inside flash memory a hidden storage region for storing special data and a key code, in addition to a main storage region for storing ordinary data. This hidden storage region is a one-time programmable memory, and is a storage region that cannot be used by ordinary users.
FIG. 1 is a diagram for explaining unauthorized copying prevention, and unauthorized copying. In flash memory, there are provided a main storage region 1 for storing ordinary data, and a hidden storage region 2 for storing special data, and furthermore, there is provided a write protect circuit 3, which prohibits the rewriting of stored data inside a hidden storage region 2. In addition thereto, flash memory is equipped with circuits required for writing (programming), erasing, and reading.
Now, let us assume that flash memory A, B is memory obtained legally on the market, and that flash memory X is memory that has been obtained illegally. In the flash memory A, B marketed legally, key codes A, B have been written to the respective hidden storage regions 2, and the respective write protect circuits 3 are in the protect mode, which prohibits rewriting. Now then, for example, when predetermined music data is stored in flash memory A, data A is encrypted in accordance with key code A, and this encrypted data A is stored in the main storage region 1. Then, when music data A is played back, data A is read out, decoded by key code A, and the decoded music data thereof is played.
Conversely, when music data A is illegally copied to flash memory B, key code A-encrypted data A is copied inside the main storage region 1 of flash memory B. Consequently, when an attempt is made to play back this illegally copied music data A, the original music data A cannot be acquired by decoding by key code B inside the hidden storage region 2 of flash memory B, and in the end, cannot be played back.
The same technique can be used to prevent the illegal use of information by unauthorized copying in the case of predetermined data or programs instead of music data.
However, if flash memory X of a state, wherein a key code is not written into the hidden storage region 2 at shipment, is illegally placed on the black market, the above-mentioned unauthorized copying prevention function is lost. That is, by storing in respective regions 1, 2 of an illegally obtained flash memory X both key code A of inside a hidden storage region 2, and data A encrypted inside a main storage region 1 of a flash memory A, in which is stored legally encrypted data A, it is possible to illegally copy and illegally use data A.
Therefore, there is need for a nonvolatile semiconductor memory that is capable of preventing the unauthorized copying of data, and the unauthorized use of data in line therewith, even when same is illegally sold on the black market as-is without being programmed with a with a special code in the hidden storage region 2 as described above.